In the machine weaving and knitting of fabric, defects occur due to missed stitches, loops and knots, apparatus malfunctioning, misalignment, or other reasons, and such defects, if occasionally occurring at random, are accepted as an economic necessity. However, frequently recurring defects such as produced by broken needles or apparatus, snags, etc., will cause a fabric machine to produce unacceptable material, and if the malfunction is not quickly remedied considerable scrap material is produced, and the likelihood of more serious damage to the knitting or weaving machine is present. Previously, most machine knitting and weaving fabric was visibly inspected, but due to the fact that one operator was responsible for a number of machines considerable material waste was produced due to breakage or malfunction.
Defect detection apparatus has been developed for fabric producing machines, and such apparatus may use light reflection techniques for scanning fabric as shown in U.S. Pat. Nos. 3,160,759; 3,589,816; 3,786,265; 4,057,351; 4,075,498 and 4,103,177. Additionally, it is known to use scanning apparatus employing light frequencies other than visible frequencies and infrared and ultraviolet band frequencies have been employed as shown in U.S. Pat. Nos. 3,206,606; 3,325,649; 3,551,678 and 3,994,586.
Inspection apparatus such as that shown in the aforementioned patents is capable of sensing defects, however, such prior art devices do not have the capability to determine when the rate of occurrence of defects is acceptable or objectionable, and such apparatus which terminates knitting or weaving machine operation upon the sensing of a single defect reduces the machine's output to unacceptable low levels. There is the need for automatic fabric inspection apparatus which is capable of analyzing the defect characteristics and determining when the rate of defect occurances is tolerable and intolerable with respect to the rate of production and the quality of product desired. Prior art devices are incapable of meeting this need.
It is an object of the invention to provide fabric defect detection apparatus capable of detecting fabric defects and producing a signal wherein the number of defects occurring may be counted and retained.
A further object of the invention is to provide fabric defect detection apparatus utilizing infrared band scanning wherein fabric defects produce an electronic signal which is retained and counted, and timing apparatus is associated with the counting and retaining apparatus whereby a control signal is produced upon a predetermined number of defects occurring within a predetermined time interval so as to permit a given quality of product to be automatically maintained.
An additional object of the invention is to provide fabric defect detection apparatus capable of simultaneously scanning a signficant portion of the fabric wherein an electronic signal is produced upon a defect being detected, the apparatus being capable of recognizing the same defect upon being repetitiously sensed, and rejecting such repetitious sensing of a common defect as a plurality of defects for machine control purposes.
A further object of the invention is to provide fabric defect detection apparatus which is electronically controlled, is capable of retaining and counting defect signals, and uitlizes timer apparatus wherein the number of defects occurring in a predetermined time frame are sensed, the timer apparatus being initiated by a defect occurring, and the timer apparatus being reset upon termination of the predetermined time interval.
In the practice of the invention a sensing head of elongated length, such as 5 inches, is located adjacent a moving fabric which has just been knitted or woven by conventional fabric producing apparatus. The fabric being sensed may be moving as a linear web, or the fabric may be in the form of a tube which is rotating. The sensing apparatus is located adjacent the newly manufactured fabric and includes an infrared light source illuminating the portion of the fabric being sensed by infrared light detecting means. The detecting means consists of a block having a plurality of light receiving openings defined therein, and a sensitive, electronic, infrared, light detector being located adjacent each light passage wherein the passing of a defect past a fabric portion reflecting light into a given passage will cause a variation in the amount of light reflected into that passage producing an electronic variation in the light receiving sensor to produce an electronic signal.
The electronic signal produced due to a defect passing the sensor is amplified, compared with a background control signal, filtered, and electronically counted. The electronic counting apparatus is also associated with an electronic timer whose time frame is initiated by the first counted defect being sensed, and as subsequent defects are signaled during an initiated time frame such defects are counted and if the number of defects occurring within the predetermined time frame is greater than a predetermined number the apparatus will be automatically stopped, and adjustments will be made by the operator to correct the problem.
The electronic timer includes means for varying the duration of the time frame during which defects are counted, and thus, it will be appreciated that the apparatus is capable of closely regulating the quality of the fabric being produced in that the number of defects acceptable within a predetermined time interval regulates the quality of the product, and should the rate of defect occurrence exceed that desired the apparatus will automatically shut down and not produce scrap material. The fact that the apparatus is capable of continually determining and evaluating the quality of the fabric being manufactured prevents excessive attention to the equipment, as is the case with fabric defect detection devices which stop the knitting or weaving machine upon a single defect occurring.
The defect detection apparatus also includes means for analyzing the defect signals it receives in that repetitive signals may mean that the sensor is repeatedly detecting the same defect, as when the advance of the fabric is less than the length of the sensing array, and the circuit of the invention would count such signals as a single defect and thereby prevent unnecessary machine shut-down.
The circuit of the defect detection system of the invention includes means for automatically sensing the reflecting characteristics of the fabric being sensed to reflect infrared light and automatic background control means are used to modify the circuit with respect to this fabric characteristic so as to achieve a uniformity of circuit operation regardless of the reflectance of the fabric being sensed.
The defect detection apparatus includes means for analyzing the defect signals it receives, in that repetitive signals may mean that the sensor is repeatedly detecting the same defect, e.g. a run, and the circuit of the invention would shut down the machine to prevent production of unacceptable material.
The defect detection system also includes signal producing means for counting the total number of defects that occur, and also is conscious of repetitive defects for terminating machine operation. Likewise, the circuit may include a large hole detector wherein a single large defect such as produced by a major machine malfunction can be quickly detected to deactivate the fabric producing machine.